Free cutting alloy



Patented 8, 1935 UNITED STATES FREE CUTTING ALLOY Howard L. Hopkins, Cleveland, Ohio, aasignorto Aluminum Company of America, Pittsburg Pa., a corporation of Pennsylvania Y No. Drawing.

Application September 18, 1933, Serial No.- 689,891 a 2 Claims. (01. 15-1) The invention relates to aluminum-copper alloys and is particularly concerned with alloys of this nature containing substantial amounts of bismuth. j

Despite the manifold advantages connected with the use of aluminum and its alloys in commercial fields, there is an inherent drawback which somewhat curtails their use in certain potential applications. Aluminum alloys, for inlo stance, containing from about 4 per cent to about 12 per cent of copper have a wide range of usefulness onaccount of their favorable mechanical properties in the cast or wrought condition and their susceptibility to improvement or .variation 15 of physical properties by suitable thermal treatments. These alloys, within various composition ranges, may be rolled, drawn, forged, extruded, or otherwise mechanically deformed. The grain is thereby refined and the physical properties considerably improved. The inherent disadvantage hereinabdve mentioned consists in the fact that machining operations such as boring, drilling, shaping, planing, or lathe-cutting are most successfully carried out only by using certain precautions which increase the expense of the operation and which occasionally force the substitution of another alloy more. readily machinable but otherwise not so desirable from the standpoint of physical properties. When alloys are i dimcult to m'achine this disadvantage becomes evident in many cases through rapid wear of the cutting tool edge which necessitates frequent resharpening. In such cases where machining is difficult continual lubrication is required, the machined surface is rough and irregular and the chip has a tendency to form long curls or spirals that may foul the tool or operating parts of the machine. The need is thus immediately apparent for an alloy of good working characteristics and satisfactory physical properties yet possessing favorable machining qualities so that articles of good surface appearance may be formed therefrom economically and successfully; An alloy satisfying these requirements may, for convenience, be styled free machining or free cutting and alloying constituents added to-accomplish the desired results may be termed "free machining constituents".

Accordingly an object of this invention is the production of an aluminum base alloy containing from about 4 per cent to about 12 per cent of copper which exhibits free cutting characteristics. A further object is the production of such an alloy which possesses physical properties equal 'main amenable to extrusion processes. Aluminum base alloys containing from about 4 per cent to about 12 per cent of copper may be readily cast in sand or permanent molds. In the lower cop-g 15- per range such alloys are used, for instance, as screw-machine products such as bolts, nuts. and screws, while automotive parts such as crankcases or pistons, may be cited asapplications of the casting art in the higher copper range. Both of these adaptations, and more especially the screw-machine products require a high degree of machinability for economical commercial production. Such applicationshave heretofore been attended by the diflicultiesand disadvantages 25 hereinabove set forth as consequent upon inferior .machining characteristics. 'ZBy preparingalloys in accordance with my invention the aluminumcopper type of alloy is rendered considerably more amenable to machining operations. The chips flow more freely from the article being cut, they are more breakable, and are less objectionable in nature than chips from the same alloy containing no bismuth. The machining operations can also be performed more rapidly and econom- 35 ically, with a resulting machined surface that has a bright, smooth, pleasing appearance.

The addition of between about 0.05 and 1.5 per cent bismuth does not appear to affect the mechanical properties of the almninum-copper alloys or disadvantageously influence other desirable qualities such as casting or working characteristics. .It thus becomes possible to accommodatethe aluminum-copper alloys to varying situations and needs without particular reference to the effect of di'iferent amounts of the free machining constituent-while retaining the advantage of an improvement in machining characteristics. 1 1 50 Within the composition range hereinbefore' disclosed I have found that the following alloy embodies preferred characteristics: An alloy of 6 per cent copper, 1.0 per cent bismuth, balance substantially ahuninum. As a general rule the scribed ,in co-pending application,

amount of free machining constituent may be reduced as the copper content is increased.

The bismuth may be added most conveniently by dropping it in solid metallic form into a molten heat of aluminum-copper alloy and thoroughly stirring the same as is more fully de- Serial No.

The melting point oi bismuth is considerably below that oi. aluminum-copper alloys so that it becomes molten almost immediately.

- The alloys within the scope of this invention are amenable to the usual thermal treatments suited to' aluminum-copper alloys, and now iamiliar to the art.

The term aluminum-copperalloy" as used herein and in the appendedclaims embraces those aluminum alloys containing more than 50 melting practice. I 1

I claim:

1. An aluminum-copper alloy containing from about 4 per cent to about 12 per cent of copper and between about 0.05 per cent and 1.5 per cent bismuth, the balance being substantially aluminum.

2. An aluminum-copper alloy containing about 6 per cent of copper and about 1.0 per cent of bismuth, the balance of stantially aluminum.

HOWARD L. norms.

the alloy being subi 

